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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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package com.oracle.svm.core.genscavenge;

import org.graalvm.nativeimage.Platform;
import org.graalvm.nativeimage.Platforms;
import org.graalvm.word.Pointer;
import org.graalvm.word.UnsignedWord;

import com.oracle.svm.core.graal.meta.SharedRuntimeMethod;
import com.oracle.svm.core.heap.ObjectReferenceVisitor;
import com.oracle.svm.core.heap.ReferenceAccess;
import com.oracle.svm.core.hub.DynamicHub;

import jdk.vm.ci.meta.SpeculationLog.SpeculationReason;

class RuntimeCodeCacheReachabilityAnalyzer implements ObjectReferenceVisitor {
    private boolean unreachableObjects;

    @Platforms(Platform.HOSTED_ONLY.class)
    RuntimeCodeCacheReachabilityAnalyzer() {
    }

    public void initialize() {
        this.unreachableObjects = false;
    }

    public boolean hasUnreachableObjects() {
        return unreachableObjects;
    }

    @Override
    public boolean visitObjectReference(Pointer ptrPtrToObject, boolean compressed) {
        assert !unreachableObjects;
        Pointer ptrToObj = ReferenceAccess.singleton().readObjectAsUntrackedPointer(ptrPtrToObject, compressed);
        if (ptrToObj.isNonNull() && !isReachable(ptrToObj)) {
            unreachableObjects = true;
            return false;
        }
        return true;
    }

    public static boolean isReachable(Pointer ptrToObj) {
        assert ptrToObj.isNonNull();
        UnsignedWord header = ObjectHeaderImpl.readHeaderFromPointer(ptrToObj);
        ObjectHeaderImpl ohi = ObjectHeaderImpl.getObjectHeaderImpl();
        if (ohi.isForwardedHeader(header) || ohi.isBootImageHeader(header)) {
            return true;
        }

        Space space = getSpace(ptrToObj, header);
        if (space == HeapImpl.getHeapImpl().getOldGeneration().getToSpace()) {
            return true;
        }

        Class<?> clazz = DynamicHub.toClass(ohi.dynamicHubFromObjectHeader(header));
        return isWhitelistedClass(clazz);
    }

    private static Space getSpace(Pointer ptrToObj, UnsignedWord header) {
        if (ObjectHeaderImpl.getObjectHeaderImpl().isAlignedHeader(header)) {
            AlignedHeapChunk.AlignedHeader chunk = AlignedHeapChunk.getEnclosingAlignedHeapChunkFromPointer(ptrToObj);
            return chunk.getSpace();
        } else {
            UnalignedHeapChunk.UnalignedHeader chunk = UnalignedHeapChunk.getEnclosingUnalignedHeapChunkFromPointer(ptrToObj);
            return chunk.getSpace();
        }
    }

    /**
     * Checks if the unreachable object is one of the following whitelisted classes:
     * <ul>
     * <li>{@link SpeculationReason} objects are embedded in the code and only needed when a
     * deoptimization is triggered.</li>
     * <li>{@link SharedRuntimeMethod} objects are sometimes used as artifical methods (e.g., for
     * adapter code) and are located in the frame info object constants.</li>
     * </ul>
     */
    private static boolean isWhitelistedClass(Class<?> clazz) {
        return SpeculationReason.class.isAssignableFrom(clazz) || SharedRuntimeMethod.class.isAssignableFrom(clazz);
    }
}
